VIDEO confession: Men shown on a video grab first made public in 2005 admit to being members of the Zetas, a group of drug traffickers whose presence is felt deeply in the Mexican border city of Nuevo Laredo, across from Laredo, Texas.

NUEVO LAREDO, Mexico For all the beefed-up enforcement along the border, the militia-like group of drug-cartel enforcers known as the Zetas appears stronger than ever, a result of better training, successful recruiting in Central America and continued desertions from the Mexican military, U.S. intelligence officials say.

The Zetas have again become entrenched in Nuevo Laredo, and they practically control the movement of people through an intricate web of spies, checkpoints and skillful use of technology, U.S. and Mexican authorities say.

Last year, U.S. and Mexican authorities reported that the number of Zetas was falling rapidly, the result of both government pressure and ongoing warfare with rival cartels. But the shadowy group of elite former military officers, soldiers and others has now grown to more than 500 nationwide, with hundreds more in a support network throughout the country, U.S. officials said.

A shootout last week between Zetas and members of the Mexican military – reportedly acting on tips from the Sinaloa cartel – involved grenades and bazookas in a residential neighborhood of Nuevo Laredo, U.S. authorities said. The firefight killed four people suspected of drug trafficking – believed to be Zetas – and injured at least four others, authorities said.

The report could not be independently confirmed.

The Zetas, enforcers of the gulf cartel, are battling rival members of the Sinaloa cartel for drug distribution routes, including the Interstate 35 corridor into Texas.

U.S. authorities said the gulf cartel has established training camps in the border states of Tamaulipas – its base of operations – and Nuevo Leon, and in the central state of Michoacán. The organization is recruiting former Guatemalan special forces military personnel known as Kaibiles and members of the notorious cross-border gangs known as Maras, including the violent Mara Salvatruchas with ties to El Salvador.

“The resiliency and determination of these criminals are beyond anything I have seen in my years in U.S. law enforcement,” said one U.S. intelligence official, speaking on condition of anonymity. “They’re tough, and they won’t break easily. They pose a serious threat to Mexico and to security along the border.”

U.S. and Mexican authorities met in Laredo recently to discuss what one official described as Mexico’s “grave” security situation, including the killing of a judge and three senior law-enforcement officials. In the meeting, U.S. authorities pressed Mexico to return a large number of federal troops to Nuevo Laredo.

Federal troops occupied the city for several months last year when the entire police force was suspended in an effort to rid the department of corrupt officers working on behalf of the drug cartels. But the program, dubbed “Secure Mexico,” was considered a failure and scrapped, Mexican authorities concede.

“We also offered every possible support to Mexico to help apprehend those who murder law-enforcement, judicial or investigative officers here because of their efforts to enforce the law in Mexico,” U.S. Ambassador Tony Garza said of the Laredo meeting. “Uniting forces between our two countries is crucial if we are to send a clear message to all criminals … that we will not tolerate violence on either side of our border.”

A senior U.S. official described the meeting as positive. “This was the first time I saw our Mexican counterparts sincerely worried about the situation,” the official said.

The Mexican government has not issued a statement, and authorities wouldn’t discuss the meeting, although Mexico’s top organized-crime investigator, Jose Luis Santiago Vasconcelos, said last week, “We know what the situation is, and we don’t need anyone else to tell us what it is.”

U.S. intelligence officials along the U.S.-Mexico border say the resurgence of the Zetas has to do in part with the desertion of soldiers from the Mexican military.

In a hearing before Mexico’s Senate in July, Gen. Gerardo Clemente Vega Garcia said more than 100,000 soldiers have deserted over the past six years, although he said he didn’t know how many may have defected to drug cartels. He listed, among other factors, “money, the lifestyle and women” as reasons for desertion to organized crime.

The Zetas are now getting “bigger and bigger,” with a growing presence not just in their base of Tamaulipas, along the Texas-Mexico border, but also in the states of Nuevo Leon, Chiapas, Quintana Roo, Tabasco, Guerrero, Veracruz, Michoacan and Jalisco, the U.S. intelligence official said.

The Zetas even have a Cuban spiritual leader who performs Santeria rituals, U.S. authorities said, and they invest about 50 percent of their earnings in training, recruiting, intelligence-gathering and computer software.

“They have the Texas-Mexico border wired,” the U.S. intelligence official said, and they use Web logs for recruiting – “although there’s nothing more effective than personal recommendations.”

The rival Sinaloa cartel also trains and recruits Central Americans, “although they generally depend more on the corruption within the government for help. This includes federal agents and members of the military,” the official said.

Nowhere is the Zetas’ presence more deeply felt than in Nuevo Laredo.

The number of drug-related killings in the border city across from Laredo, Texas, has surpassed 160 this year, compared with 182 for all of 2005.

About 200 Zetas operate in the city, with a support system of about 300 people, including lookout guides known as halcones, the officials said.

Additionally, they depend on members of the municipal police, who earn about $500 every two weeks, U.S. authorities say.

The city is still without a police chief. Chief Omar Pimentel resigned in February after serving six months in the job. His predecessor, Alejandro Dominguez, was gunned down just hours after being sworn in.